Field of the Invention
The present invention relates to image processing for an image restoration.
Description of the Related Art
Since an image captured through an image pickup optical system may blur and deteriorate due to influence of aberrations of the image pickup optical system, etc., an image restoration is conventionally applied so as to correct the deterioration. The image restoration can be executed with a software operation or a hardware operation. The software operation generally requires a personal computer (“PC”) and thus the hardware operation is advantageous to the image restoration in an image pickup apparatus.
The hardware operation relies on an integer operation, and the number of digits is set to 16 or 32 bits, or the like, which can be processed. The image restoration also use a plus or minus code and a decimal value. For example, the first bit is configured to express a plus or minus code, and the fixed-point arithmetic is used to fix a position of the decimal point between the integer part and the decimal part. The calculation that exceeds the digits of the integer part results in an overflow. The overflow is likely to occur in the inverse Fourier transform in generating an image restoration filter.
Japanese Patent Laid-Open No. (“JP”) 2011-60177 discloses a fast Fourier transform (“FFT”) operating unit having a plurality of operating parts for an FFT with the fixed-point arithmetic having a fixed bit length. This FFT operating unit provides a bit shift to at least one operating data of the operating part, and at least one operating part serves to detect its overflow. The FFT operating unit adjusts a bit shift amount when the overflow is detected by the operation part.
However, the method of JP 2011-60177 changes a bit assignment of the decimal part in the calculation and cannot guarantee the desired calculation precision.